We have prepared monoclonal antibodies against a series of biologically important glycoproteins isolated from the cell surface of chinese hamster ovary cells as well as a number of other cell types. We are using these antibodies in our on-going investigations into the molecular mechanism(s) controlling the mobility of glycoproteins on the cell surface. In this work we are employing fluorescence and scanning electron microscopy in association with indirect immunoassays to localize surface antigens to specific domains on the cell surface as well as to evaluate the redistribution of the particular surface antigen which may occur in the presence of antibody. We are also using our monoclonal antibodies to investigate the biosynthesis and mode of intercalation of glycoproteins and proteoglycans into the membrane of cells maintained in culture. Finally we are using the monoclonal antibodies as agents for selecting cell variants which lack particular cell surface glycoproteins. By isolating such variants it should be possible to identify the function of individual cell surface glycoproteins, a task which has, to date, eluded most workers.